Since an aromatic polycarbonate resin has excellent mechanical properties and thermal properties, it is used in a wide variety of industrial fields. However, the aromatic polycarbonate resin is inferior in moldability since it has poor flowability due to its high melt viscosity. To improve the flowability of the aromatic polycarbonate resin, a large number of polymer alloys of the aromatic polycarbonate and another thermoplastic resin have been developed. Out of these, a polymer alloy of the aromatic polycarbonate and a styrene-based resin typified by ABS resin is widely used in fields such as OA equipment, electronic and electric equipment and automobiles. Requests for the flame retardation of resin materials which are mainly used in OA equipment and home electric appliances in particular have been strong. To meet the requests, studies have been made on a polymer alloy of an aromatic polycarbonate resin and ABS resin so as to satisfy the requirement for the flame retardation of a thin molded article, for example, UL94 5VB which is a safety standard required for large-sized products.
A combination of a halogen-based flame retardant containing bromine and a flame retarding aid such as antimony trioxide has generally been used for the flame retardation of the polymer alloy. For example, as for 5VB flame retardation, there is proposed a method in which a flame retardant and a flame retarding aid are added to a blend of an aromatic polycarbonate resin and ABS resin and then polytetrafluoroethylene having fibril formability and an inorganic filler having specific L/D such as talc is added (refer to JP-A 2-199162).
However, studies into flame retardation by using an organic phosphorus-based flame retardant containing no halogen-based compound having bromine are now actively under way due to a problem such as the production of a harmful substance at the time of combustion. For example, a large number of compositions obtained by adding an organic phosphorus-based flame retardant and further polytetrafluoroethylene having fibril formability to a polymer alloy of an aromatic polycarbonate resin and ABS resin have been proposed, and information related to these is widely known (refer to JP-A 2-115262).
The method of improving flame retardancy by mixing a polycarbonate-organopolysiloxane copolymer resin with an aromatic polycarbonate resin is disclosed by Japanese Patent No. 3037588. However, a polycarbonate resin composition comprising no flame retardant is unsatisfactory in achieving flame retardancy as high as UL94 5VB required for large-sized equipment such as OA equipment when it is thin though it is excellent in heat stability and long-term heat resistance. Although the method of improving flame retardancy by mixing a phosphoric acid ester with an aromatic polycarbonate resin containing a predetermined amount of silicon and a polycarbonate-organopolysiloxane copolymer resin is disclosed by Japanese Patent No. 3457805, since a small amount of the phosphoric acid ester is used and no silicate mineral is added, UL94 5VB rating is not attained when the resulting mixture is thin. Further, although the method of improving flame retardancy by mixing an organic sulfonic acid metal salt is disclosed by JP-A 8-302178, the improvement of a flame retarding effect to some extent is observed but the method is unsatisfactory in achieving flame retardancy as high as UL94 5VB which is required for large-sized equipment such as OA equipment when the resulting mixture is thin. Also, a halogen-free, phosphorus-free flame retarding effect obtained by mixing a silicone-based flame retardant containing a functional group and an inorganic filler with a polycarbonate resin, a polycarbonate-polydiorganosiloxane copolymer resin and a styrene-based resin is disclosed (refer to Japanese Patent No. 3616791). However, although the silicone-based flame retardant provides flame retardancy while heat resistance is retained, it is unsatisfactory in achieving flame retardancy as high as 5VB when the obtained mixture is thin.
JP-A 2004-35587 also discloses a resin composition which comprises an aromatic polycarbonate resin, a styrene-based resin, an alkali metal salt and/or an alkali earth metal salt, a silicone compound containing a functional group, an inorganic filler and a polytetrafluoroethylene resin. However, this publication does not teach that flame retardancy as high as 5VB can be attained when the resin composition is thin.
Although resin compositions having certain flame retardancy comprising a polycarbonate-polydiorganosiloxane copolymer resin are disclosed as described above, a resin composition having flame retardancy as high as UL94 5VB when the resin composition is thin is desired but not obtained yet.